This invention relates generally to valves for controlling fluid flow. More particularly, the invention relates to valves for metering fluid flow manually and with electronic means.
Almost all valves consist of a fixed body containing a hole or port covered by a sealing element. This sealing element (valve) can uncover the port to varying degrees and allow fluid to flow. The arrangement of these elements generally takes the form of axial pairs (lift valve), turning pairs (rotary valve motion), screw pairs (helical valve motion), and sliding pairs (gate valve). These valve elements are accepted practice, have been utilized for centuries and there are many manufacturers using these principles to accomplish the same task.
The miniature valve market, typified by manufacturers like Clippard, Pneumadyne and Whitey, offer a variety of metering valves. However, all are needle valve designs. Needle valves are capable of precise metering but have several drawbacks. A needle valve is an axially arranged device and its accommodation to applications usually require shapes, ports and manufacturing complexity. In order to adjust flow rates a tapered needle is screwed in and out of a circular aperture enabled by threads coaxially constructed along the needle shaft. The resulting space offered as a flow passage is at best an annulus (and often deteriorates to a crescent) where the area varies with axial needle position created by screw threads. Area is an arithmetic function of the radii squared and accordingly the range of linear sensitive control is only approximate and at the same time narrow. Also, unless the same material is used throughout, the valve differential expansion leads to an inherent lack of temperature compensation. Furthermore, the tiny clearances generated clog easily and good filtration of the medium is required. Unless exceptionally complex shapes, and/or threads and/or controls are used in the design of the valve, the flow through needle valves is not a linear function of needle position. The needles themselves require precision manufacturing techniques. Since the needle requires several rotations from off to fully open they do not lend themselves to rapid automatic operation. It is also very difficult to arrange a needle valve for xe2x80x9cfail safexe2x80x9d operation, i.e., should the valve actuator loose power, the valve cannot be spring or gravity returned to the off position. Moreover, the needle and seat surfaces are subject to damage due to brinelling scuffing and scoring.
Accordingly, there is a need for a valve that solves the problems associated with needle, ball and butterfly, valves. It is among the objects of the invention to provide a valve that simplifies manufacturing requirements. Another object of the invention is to provide a valve the provides a linear response curve. A further object is to provide a valve that allows for customized flow resistance versus valve position. These and other objects will become apparent from a reading of the following summary and detailed description of the illustrative embodiment.
The invention described herein overcomes several of the drawbacks found with competing devices and offers added versatility and ease of manufacture. The valve is an extreme case of rolling hypocycloidal motion which is the geometric name given to a circle rolling inside a larger circle. In this configuration, the inner circle is 5 to 20% smaller in diameter than the outer circle that includes or contains the control xe2x80x9cOxe2x80x9d ring. Thus, the seal device not only exhibits this hypocycloidal action but also has a small amount of sliding.
The larger diameter or circle utilizes the inner diameter of an xe2x80x9cOxe2x80x9d-ring as the throttling or control surface, captured in either a plain circular groove or a uniquely shaped groove as the controlling valve element. This xe2x80x9cOxe2x80x9d-ring/groove combination is eccentric to the center spindle that contains the valve port and also serves as a channel for directing the fluid to be metered. When off, due to the local squeeze or flattening of the xe2x80x9cOxe2x80x9d-ring the sealing is accomplished by covering or blocking the valve port and produces a bubble-tight seal. A the sleeve containing the xe2x80x9cOxe2x80x9d-ring/groove is rotated about the spindle, the eccentricity of the groove allows the xe2x80x9cOxe2x80x9d-ring to gradually uncover the valve port thereby permitting flow of the upstream pressurized fluid. The extreme positions start from 0 degrees where the port(s) are fully covered to about 180 degrees where the maximum amount of clearance above the port(s) exists. As rotation continues beyond 180 degrees the flow begins to be restricted until at the full 360 degrees the port(s) are completely covered. In other words, the full range of flow modulation takes place over 180 degrees of the outer sleeve rotation and the control is the same for either direction of rotation. In practice, the most useful range of rotation is usually about 90 degrees from fully xe2x80x9coffxe2x80x9d to maximum useful flow. The geometric nature of the eccentric groove and the proportions of the xe2x80x9cOxe2x80x9d-ring cross sections with respect to the port sizes create a flow pattern that is approximately sinusoidal but approaching linear with respect to the angle of rotation.
In practice, due to tolerances, deformation of the xe2x80x9cOxe2x80x9d-ring seal effective control range is about 90 degrees (xc2xc turn) of rotation, where the valve goes from shut to fully open. This arrangement has numerous advantages over needle valve designs. Further, by machining unique shapes for the gland containing the xe2x80x9cOxe2x80x9d-ring (easily achieved with modern CNC (computer numeric control) machine tools), the resistance curve of the valve can be tailored to the application. In addition, the sealing surfaces tend to be inherently self-flushing or cleaning, tolerant of debris and insensitive to vibration. In choosing the port of the appropriate size, the maximum resistance of the valve can set to the desired valve. Unlike other xc2xc turn valve types (butterfly valves and ball valves), the invention has precision incremental metering characteristics. The internal geometry of ball valves and butterfly valves causes them to open and close very abruptly and thus makes them ill suited to accurately meter flow rates (although they are often used in such applications).
The invention has an inherently gradual open/close cycle. Since it can be shut off within xc2xc turn in one embodiment, the valve can be made xe2x80x9cfail-safexe2x80x9d by the addition of a spring return. All of these features can be achieved by modification of two machined parts.